Fuel cell systems enable low-emission, highly efficient generation of electric current. For this reason, efforts are currently being made to use fuel cell systems to generate electrical energy in various mobile applications, such as for example in automotive engineering or aeronautics. It is, for example, conceivable in an aircraft to replace the generators, which are currently used to supply power on board and are driven by the main engines or the auxiliary power unit (APU), with a fuel cell system. A fuel cell system, moreover, might also be used to supply the aircraft with emergency power and replace the ram air turbine (RAT) hitherto used as an emergency power system.
Besides electrical energy, a fuel cell during operation generates thermal energy, which has to be removed from the fuel cell with the aid of a cooling system in order to prevent overheating of the fuel cell. A fuel cell system installed in an aircraft, for example for the on-board power supply, therefore has to be designed in such a way that it is capable of meeting a high demand for electrical energy. A fuel cell that has a high capacity for generating electrical energy, however, also generates a large amount of thermal energy and therefore has a high cooling requirement. Moreover, on board an aircraft a large number of further technical devices are provided, which generate heat and have to be cooled in order to guarantee reliable operation. These technical devices include, for example, the air conditioning units or the electronic control components of the aircraft.
Currently employed aircraft cooling systems normally comprise air inlet openings provided in the region of the aircraft outer skin which can be configured, for example, as ram air inlets and serve to convey ambient air as coolant into the aircraft cooling system. Cooling air warmed by absorbing heat from devices to be cooled on board the aircraft is usually led back into the environment through air outlet openings likewise provided in the region of the aircraft outer skin. The air inlet and air outlet openings formed in the aircraft outer skin, however, increase the aerodynamic drag and thus the fuel consumption of the aircraft. Moreover, aircraft cooling systems supplied with cooling air via ram air inlets have high pressure losses, a cooling capacity limited inter alia by the maximum supply air volume flow through the ram air inlets, and a relatively high weight.